The Financial Services Authority, the UK regulator, is to investigate dealings in the shares of Amvescap, the Anglo-US fund manager whose price plunged more than 8% this morning after Canadian predator CI Financial said it was pulling a potential offer.

On Monday CI Financial said it was prepared to go hostile. Today it said that "it cannot develop an offer proposal at this point in time without the full cooperation of Amvescap...given its recent performance which was highlighted in the interim results."